Medial temporal lobe structures and autism: a review of clinical and experimental findings

Tuberous sclerosis complex: correlation of magnetic resonance imaging (MRI) findings with comorbidities

We studied the magnetic resonance imaging (MRI) findings in a cohort of Chinese children with tuberous sclerosis complex to determine the relationship between age, sex, mental retardation, autism, epilepsy, infantile spasm, and early age at onset of seizures and the numbers and locations of tubers detected. We searched our tuberous sclerosis registry, established in 1985 (N = 44), and performed an analysis of children who had MRIs of the brain performed (n = 22). A neuroradiologist blinded to the clinical findings scored the MRIs according to the total number and site of the tubers. The following factors were analyzed: age, sex, presence of autism (n = 7), presence (n = 19) and severity of mental retardation (mild [n = 12], moderate to severe [n = 7]), presence of epilepsy (n = 21) or infantile spasm (n = 8), and age at onset of seizures less than 1 year (n = 10). There was no significant relationship between the number and site of tubers and the following factors: sex, autism, mental retardation, degree of mental retardation, epilepsy, history of infantile spasm, or age at onset of seizures less than 1 year. Only the presence of cortical tubers in the parietal regions had a significant relationship with the history of infantile spasm (P = .012). Using multiple regression analysis of all of the risk factors, only age is related to the number of tubers in the MRI (P = .047), and a history of infantile spasm is related to the presence of tubers in the parietal (P = .009) and occipital (P = .031) lobes. The associated comorbidities in tuberous sclerosis complex might be explained by more complex underlying genetic or pathologic issues rather than purely by the site of the cortical tubers. We suggest that a developmental approach, by analyzing the age at the appearance of tubers in both symptomatic and asymptomatic cases with the development of other neuropsychiatric comorbidities, should be undertaken to assess the causal relationship.

Contributions of the Amygdala to Emotion Processing: From Animal Models to Human Behavior

Research on the neural systems underlying emotion in animal models over the past two decades has implicated the amygdala in fear and other emotional processes. This work stimulated interest in pursuing the brain mechanisms of emotion in humans. Here, we review research on the role of the amygdala in emotional processes in both animal models and humans. The review is not exhaustive, but it highlights five major research topics that illustrate parallel roles for the amygdala in humans and other animals, including implicit emotional learning and memory, emotional modulation of memory, emotional influences on attention and perception, emotion and social behavior, and emotion inhibition and regulation.

The orbitofrontal-amygdala circuit and self-regulation of social-emotional behavior in autism

Individuals with an autistic spectrum disorder are impaired not only in understanding others' mental states, but also in self-regulation of social-emotional behavior. Therefore, a model of the brain in autism must encompass not only those brain systems that subserve social-cognitive and emotional functioning, but also those that subserve the self-regulation of behavior in response to a changing social environment. We present evidence to support the hypothesis that developmental dysfunction of the orbitofrontal-amygdala circuit of the brain is a critical factor in the development of autism and that some of the characteristic deficits of persons with autism in socio-emotional cognition and behavioral self-regulation are related to early dysfunction of different components of this circuit. A secondary hypothesis posits that the degree of intellectual impairment present in individuals with autism is directly related to the integrity of the dorsolateral prefrontal-hippocampal circuit of the brain. Together, these hypotheses have the potential to help explain the neurodevelopmental basis of some of the primary manifestations of autism as well as the heterogeneity of outcomes.

Humor in autism and Asperger syndrome

Research has shown that individuals with autism and Asperger syndrome are impaired in humor appreciation, although anecdotal and parental reports provide some evidence to the contrary. This paper reviews the cognitive and affective processes involved in humor and recent neurological findings. It examines humor expression and understanding in autism and Asperger syndrome in the context of the main psychological theories (Theory of Mind, Executive Functions, Weak Central Coherence and Laterization models) and associated neural substrates. In the concluding sections, examples of humor displayed by individuals with autism/Asperger syndrome which appear to challenge the above theories are analyzed and areas for further research are suggested.

The impact of early institutional rearing on the ability to discriminate facial expressions of emotion: an event-related potential study

Event-related potentials (ERPs), in response to 4 facial expressions of fear, angry, happy, and sad, were collected from 72 institutionalized children (IG), ages 7 to 32 months, in Bucharest, Romania, and compared with ERPs from 33 children, ages 8 to 32 months, who had never been institutionalized (NIG). The NIG and IG exhibited different patterns of responding in early latency components. Moreover, group differences in amplitude were evident across all components. Such differences may point to the role of early deprivation in disrupting the development of the neural circuitry involved in the recognition of facial expressions.

Neuropeptides and non-human primate social deficits associated with pathogenic rearing experience

There is a persuasive evidence that autism is highly heritable and likely to be substantially determined by polygenic mechanisms. Nevertheless, some intriguing findings in children raised in conditions of extreme social deprivation suggest that an autistic-like syndrome may occur as a consequence of environmental conditions. A particularly close model of this human syndrome has been studied in rhesus monkeys for almost half a century. Monkeys reared in pathogenic rearing conditions manifest considerable deficits in social interaction and increased self-directed behaviors. We have been interested in the possibility that disruptions in normal social development in non-human primates might be expressed in neuropeptide systems which have emerged in rodent studies as important candidates for a unique social biology. In recent studies, we have described persistently reduced CSF OT levels in male rhesus monkeys with significant social deficits. We also found that OT levels were positively related to the expression of affiliative social behaviors. Alterations were also detected in both CRH and AVP receptor binding patterns in limbic structures likely to influence social and emotional development. Taken together, these data suggest that abnormal rearing influences the development of brain systems critical to normal social and emotional competence in rhesus monkeys and may contribute to the development of autistic-like symptomatology associated with pathogenic rearing histories.

Developmental deficits in social perception in autism: the role of the amygdala and fusiform face area

Autism is a severe developmental disorder marked by a triad of deficits, including impairments in reciprocal social interaction, delays in early language and communication, and the presence of restrictive, repetitive and stereotyped behaviors. In this review, it is argued that the search for the neurobiological bases of the autism spectrum disorders should focus on the social deficits, as they alone are specific to autism and they are likely to be most informative with respect to modeling the pathophysiology of the disorder. Many recent studies have documented the difficulties persons with an autism spectrum disorder have accurately perceiving facial identity and facial expressions. This behavioral literature on face perception abnormalities in autism is reviewed and integrated with the functional magnetic resonance imaging (fMRI) literature in this area, and a heuristic model of the pathophysiology of autism is presented. This model posits an early developmental failure in autism involving the amygdala, with a cascading influence on the development of cortical areas that mediate social perception in the visual domain, specifically the fusiform "face area" of the ventral temporal lobe. Moreover, there are now some provocative data to suggest that visual perceptual areas of the ventral temporal pathway are also involved in important ways in representations of the semantic attributes of people, social knowledge and social cognition. Social perception and social cognition are postulated as normally linked during development such that growth in social perceptual skills during childhood provides important scaffolding for social skill development. It is argued that the development of face perception and social cognitive skills are supported by the amygdala-fusiform system, and that deficits in this network are instrumental in causing autism.

Functional disconnectivity of the medial temporal lobe in Asperger's syndrome

BACKGROUND

Autistic spectrum disorders (ASD) are neurodevelopmental conditions that may be caused by abnormal connectivity between brain regions constituting neurocognitive networks for specific aspects of social cognition.

METHODS

We used three-way multidimensional scaling of regionally parcellated functional magnetic resonance imaging (fMRI) data to explore the hypothesis of abnormal functional connectivity in people with ASD. Thirteen high-functioning individuals with Asperger's syndrome and 13 healthy volunteers were scanned during incidental processing of fearful facial expressions.

RESULTS

Using permutation tests for inference, we found evidence for significant abnormality of functional integration of amygdala and parahippocampal gyrus (p < .05, false discovery rate [FDR] corrected) in people with Asperger's syndrome. There were less salient abnormalities in functional connectivity of anterior cingulate, inferior occipital, and inferior frontal cortex, but there was no significant difference between groups in whole brain functional connectivity.

CONCLUSIONS

We conclude there is evidence that functional connectivity of medial temporal lobe structures specifically is abnormal in people with Asperger's syndrome during fearful face processing.

fMRI activation of the fusiform gyrus and amygdala to cartoon characters but not to faces in a boy with autism

Abnormal hypoactivation in the amygdala and fusiform gyrus, brain areas that participate in face processing and social cognition, has consistently been demonstrated in persons with autism. We investigated activity in these areas in a boy with autism, DD, who had a special interest in "Digimon" cartoon characters. DD individuates Digimon faster than familiar faces and objects, but he individuates familiar faces no faster than objects. In contrast, a typically developing boy with an interest in "Pokemon" cartoon characters is equally fast at individuating faces and Pokemon and faster at individuating faces and Pokemon than objects and Digimon. In addition, using functional magnetic resonance imaging (fMRI), we show that DD activates his amygdala and fusiform gyrus for perceptual discriminations involving Digimon but not for those involving familiar or unfamiliar faces. This pattern of activation is not seen in the typically developing control with an interest in Pokemon or in a second comparison case who has autism but no interest in Digimon. These results have important implications for our understanding of autism, cortical face specialization, and the possible role of the amygdala in the development of perceptual expertise.

Neonatal Amygdala Lesions Affect Appetitive Motivational and Consummatory Aspects of Social Behavior in the Rat

In the present study, rats received amygdala lesions (AMX) on either Postnatal Day 7 (PD 7; immature brain) or PD 21 (almost mature brain), and adult social activity was studied after short-term isolation housing. Sham-operated rats demonstrated increased following and approaching behavior after 7 days of isolation compared with after 4 days of isolation, an effect that was absent in AMX-PD 7 and AMX-PD 21 rats. Furthermore, AMX-PD 7 rats, but not AMX-PD 21 rats, displayed a reduction in investigatory behavior after prolonged isolation. This indicates that in AMX-PD 21 rats, mainly appetitive motivational aspects of social behavior were affected, whereas in AMX-PD 7 rats both motivational and consummatory aspects were disturbed. Finally, the reported deficits in AMX-PD 7 rats may reflect neurodevelopmental deficits of structures connected with the amygdala.

Neuroanatomical substrates of social cognition dysfunction in autism

In this review article, we summarize recent progress toward understanding the neural structures and circuitry underlying dysfunctional social cognition in autism. We review selected studies from the growing literature that has used the functional neuroimaging techniques of cognitive neuroscience to map out the neuroanatomical substrates of social cognition in autism. We also draw upon functional neuroimaging studies with neurologically normal individuals and individuals with brain lesions to highlight the insights these studies offer that may help elucidate the search for the neural basis of social cognition deficits in autism. We organize this review around key brain structures that have been implicated in the social cognition deficits in autism: (1) the amygdala, (2) the superior temporal sulcus region, and (3) the fusiform gyrus. We review some of what is known about the contribution of each structure to social cognition and then review autism studies that implicate that particular structure. We conclude with a discussion of several potential future directions in the cognitive neuroscience of social deficits in autism.

The development of social behavior following neonatal amygdala lesions in rhesus monkeys

We examined the role of the amygdala in the development of nonhuman primate social behavior. Twenty-four rhesus monkeys received bilateral ibotenic acid lesions of either the amygdala or the hippocampus or received a sham surgical procedure at 2 weeks of age. Subjects were reared with their mothers and were provided daily access to social rearing cohorts. The subjects were weaned at 6 months of age and then observed while paired with familiar conspecifics at 6 and 9 months of age and with unfamiliar conspecifics at 1 year of age. The subjects were also observed during daily cohort socialization periods. Neither amygdala nor hippocampus lesions altered fundamental aspects of social behavior development. All subjects, regardless of lesion condition, developed a species-typical repertoire of social behavior and displayed interest in conspecifics during social encounters. The amygdala lesions, however, clearly affected behaviors related to fear processing. The amygdala-lesioned subjects produced more fear behaviors during social encounters than did control or hippocampus-lesioned subjects. Although the heightened fear response of the amygdala-lesioned subjects was consistent across different testing paradigms and was observed with both familiar and novel partners, it did not preclude social interactions. In fact, the amygdala-lesioned subjects displayed particular social behaviors, such as following, cooing, grunting, presenting to be groomed, and presenting to be mounted more frequently than either control or hippocampus-lesioned subjects. These findings are consistent with the view that the amygdala is not needed to develop fundamental aspects of social behavior and may be more related to the detection and avoidance of environmental dangers.

Neuroplasticity and schizophrenia

This article's title is also the name of a workshop sponsored by the International Congress on Schizophrenia Research that was focused on an appraisal of the potential role of neuroplastic processes in the etiology or course of schizophrenia. The workshop brought together clinical investigators of schizophrenia and basic scientists who study various aspects of neuroplasticity, including central nervous system (CNS) development, learning and memory, and drug action. The goal was to identify special opportunities to advance knowledge and understanding of schizophrenia pathology, treatment, or prevention by applying neuroplasticity concepts as a framework to theories of the illness. Although the focus of this workshop was schizophrenia, the phenomena considered are pertinent to other disorders, such as depression and drug abuse.

Event-related brain potentials reveal anomalies in temporal processing of faces in autism spectrum disorder

BACKGROUND

Individuals with autism exhibit impairments in face recognition, and neuroimaging studies have shown that individuals with autism exhibit abnormal patterns of brain activity during face processing. The current study examined the temporal characteristics of face processing in autism and their relation to behavior.

METHOD

High-density event-related brain potentials (ERPs) were recorded to images of faces, inverted faces, and objects from 9 individuals with autism spectrum disorder (15-42 years old) and 14 typical individuals (16-37 years old).

RESULTS

With respect to a face-sensitive ERP component (N170), individuals with autism exhibited longer N170 latencies to faces than typical individuals but comparable latencies to objects. Typical individuals exhibited longer N170 latencies to inverted as compared to upright faces, whereas individuals with autism did not show differences in N170 latency to upright versus inverted faces. Neural speed of face processing, as reflected in N170 latency, correlated with performance on a face recognition task for individuals with autism.

CONCLUSIONS

These data provide evidence for slowed neural speed of face processing in autism and highlight the role of speed of processing in face processing impairments in autism.

Understanding orbitofrontal contributions to theory-of-mind reasoning: implications for autism

Autism is a lifelong developmental disorder that is associated with severe difficulties with "theory-of-mind"--the understanding that others' behaviors are motivated by internal mental states. Here, we raise the possibility that research examining the neural bases of theory-of-mind reasoning has the potential to inform researchers about the elusive functional neural impairments associated with autism. Evidence from our lab and others' suggests that theory-of-mind reasoning may be fractionated into at least two functionally and anatomically distinct neural circuits. Specifically, the ability to decode others' mental states from observable cues (such as facial expressions) may rely on contributions from the orbitofrontal/medial temporal circuit within the right hemisphere. In contrast, the ability to reason about others' mental states may rely left medial frontal regions. We conclude by reviewing evidence suggesting that the developmental roots of autism might lie in abnormal functioning of the orbitofrontal/medial temporal circuit which may, in turn, underlie the abnormal development of social-cognitive skills among individuals with autism.

Regional glucose metabolism within cortical Brodmann areas in healthy individuals and autistic patients

A new Brodmann area (BA) delineation approach was applied to FDG-PET scans of autistic patients and healthy volunteers (n = 17 in each group) to examine relative glucose metabolism (rGMR) during performance of a verbal memory task. In the frontal lobe, patients had lower rGMR in medial/cingulate regions (BA 32, 24, 25) but not in lateral regions (BA 8-10) compared with healthy controls. Patients had higher rGMR in occipital (BA 19) and parietal regions (BA 39) compared with controls, but there were no group differences in temporal lobe regions. Among controls, better recall and use of the semantic-clustering strategy was associated with greater lateral and medial frontal rGMR, while decreased rGMR in medial-frontal regions was associated with greater perseverative/intrusion errors. Patients failed to show these patterns. Autism patients have dysfunction in some but not all of the key brain regions subserving verbal memory performance, and other regions may be recruited for task performance.

Autism: a target of pharmacotherapies?

Autism is reaching epidemic proportions. The diagnosis can be made as early as 2 years of age, and autistic patients are expected to have a normal life span. Thus, in terms of the number of 'patient years', autism spectrum disorder (ASD) represents a market that is as large as that of the biggest neurological indication, Alzheimer's disease. However, despite the clear unmet medical need no effective treatment is yet available. This could be because the biology of ASD is not clearly understood and thus proper drug treatment has not been possible. However, significant advances are being made toward understanding the mechanisms of the disease. Here, we review the most recent preclinical advances in the hope that they will lead to a breakthrough in the near future.

Amygdala cyclic adenosine monophosphate response element binding protein phosphorylation in patients with mood disorders: effects of diagnosis, suicide, and drug treatment

BACKGROUND

Signal transduction abnormalities have been identified in patients with bipolar (BD) and major depressive (MDD) disorders and are targets for lithium and antidepressant drugs. A key downstream target for signal transduction pathways is the transcription factor cyclic adenosine monophosphate (cAMP) response element binding protein (CREB). Therefore, we measured the levels of phosphorylated CREB (pCREB) in the amygdala, a region critical to emotional processing and important in the pathophysiology of both BD and MDD.

METHODS

Human postmortem amygdala sections were generously provided by the Stanley Foundation Neuropathology Consortium. Samples consisted of subjects with MDD, BD, schizophrenia (SCZ), and nonpsychiatric-nonneurologic comparison subjects (n = 15 per group). Levels of pCREB were measured by immunohistochemistry, relative to total cell number.

RESULTS

There were no differences between diagnostic groups--control subjects and subjects with BD, MDD, or SCZ--but increased numbers of pCREB stained cells were found in several amygdalar nuclei in subjects who had died by suicide. In contrast, patients treated with lithium at the time of death had significantly lower pCREB levels in the same region.

CONCLUSIONS

These results suggest that CREB activity may be an important factor in the neurobiology of suicide and the well-documented antisuicidal effect of lithium.

A systems neuroscience approach to autism: biological, cognitive, and clinical perspectives

Autism is a behaviorally defined disorder characterized by a broad constellation of symptoms. Numerous studies directed to the biological substrate demonstrate clear effects of neurodevelopmental differences that will likely point to the etiology, course, and long-term outcomes of the disorder. Consistently replicated research on the neural underpinnings of autism is reviewed. In general, results suggest several main conclusions: First, autism is a heterogeneous disorder and is likely to have multiple possible etiologies; second, structural brain studies have indicated a variety of diffuse anatomical differences, reflective of an early developmental change in the growth or pruning of neural tissue, rather than localized lesions; similarly, neurochemical studies suggest early, neuromodulatory discrepancies rather than gross or localized abnormalities; and finally, there are a number of limitations on studies of brain activity that to date preclude definitive answers to questions of how the brain functions differently in autism. The large number of active research programs investigating the cognitive neuroscience of autism spectrum disorders, in combination with the exciting development of new methodologies and tools in this area, indicates the drama and excitement of work in this area.

The development of mother-infant interactions after neonatal amygdala lesions in rhesus monkeys

As part of ongoing studies on the neurobiology of socioemotional behavior in the nonhuman primate, we examined the development of mother-infant interactions in 24 macaque monkeys who received either bilateral amygdala or hippocampus ibotenic acid lesions, or a sham surgical procedure at 2 weeks of age. After surgery, the infants were returned to their mothers and reared with daily access to small social groups. Behavioral observations of the infants in dyads (mother-infant pairs alone), tetrads (two mother-infant pairs), and social groups (six mother-infant pairs and one adult male) revealed species-typical mother-infant interactions for all lesion conditions, with the exception of increased physical contact time between the amygdala-lesioned infants and their mothers. Immediately after permanent separation from their mothers at 6 months of age, the infants were tested in a mother preference test that allowed the infants to choose between their mother and another familiar adult female. Unlike control and hippocampus-lesioned infants, the amygdala-lesioned infants did not preferentially seek proximity to their mother, nor did they produce distress vocalizations. Given the normal development of mother-infant interactions observed before weaning, we attribute the behavior of the amygdala-lesioned infants during the preference test to an impaired ability to perceive potential danger (i.e., separation from their mother in a novel environment), rather than to a disruption of the mother-infant relationship. These results are consistent with the view that the amygdala is not essential for fundamental aspects of social behavior but is necessary to evaluate potentially dangerous situations and to coordinate appropriate behavioral responses.

Neonatal Amygdala Lesions and Juvenile Isolation in the Rat: Differential Effects on Locomotor and Social Behavior Later in Life

Pervasive developmental disorders such as autism are characterized by deficits in social interaction and communication. Disturbed development of limbic structures such as the amygdala might underlie these deficits. The authors examined the effects of amygdala lesions on Postnatal Day 7 and juvenile isolation (2 weeks of individual housing during Weeks 4 and 5 of life) on rat locomotor and social activity later in life. Before puberty, but more pronounced after puberty, lesioned rats displayed enhanced locomotor activity. Adult social behavior was selectively disturbed by the lesion and the isolation procedure. In particular, the combination of neonatal lesions and juvenile isolation severely disrupted social interaction. These results suggest that a combination of neonatal amygdala damage and juvenile isolation may serve as an animal model of certain psychopathological neurodevelopmental disorders, such as autism.

Autism and pervasive developmental disorders

The quantity and quality of research into autism and related conditions have increased dramatically in recent years. Consequently we selectively review key accomplishments and highlight directions for future research. More consistent approaches to diagnosis and more rigorous assessment methods have significantly advanced research, although the boundaries of the 'broader phenotype' remain to be defined and the validity of Asperger's disorder as a discrete syndrome remains controversial. Recent epidemiological studies have shown that Autism Spectrum Disorders are common, but there continues to be debate about the causes of the increase in the frequency with which autism is diagnosed. Psychological research has helped to develop new developmental models for the disorder and there have also been significant advances in the molecular genetics of autism and understanding of the underlying neurobiological processes. Areas important for future research include the study of autism as it first develops, i.e., in infants and very young children, and of specific processes (psychological and neurobiological) which underlie the disorder. Significant challenges lie ahead in evaluating the growing number of treatments for autism and in integrating the results of research into treatment and educational settings.

Associative and recognition memory for novel objects in dementia: implications for diagnosis

It has been demonstrated that patients with dementia of the Alzheimer's type show particular difficulties with a task that measures memory for object locations [R. Swainson et al. (2001) Dement. Geriatr. Cogn. Disord. 12, 265-80]. The present study followed on from this report by asking whether the deficits seen in dementia of the Alzheimer's type were specific to this condition, or whether they would also be seen in another common neurodegenerative syndrome, frontotemporal dementia. To investigate this important issue, we examined memory for object-location pairs and visual recognition memory for novel patterns using two tests, the Paired Associates Learning and Matching to Sample tasks, from the Cambridge Neuropsychological Testing Automated Battery. The performance of a subset of the patients with dementia of the Alzheimer's type described by Swainson et al., selected on the basis of age and education, was compared with matched groups of frontal variant frontotemporal dementia, semantic dementia and control subjects. In contrast to the patients with dementia of the Alzheimer's type, who showed significant impairment on both memory tests, the two frontotemporal dementia groups did not perform significantly poorer compared with control subjects on nearly all memory measures, other than 'memory score' from the paired associates learning task. These findings confirm that tests of episodic memory, especially for the location of objects in space, may be useful in the early diagnosis and differentiation of dementia of the Alzheimer's type.

The amygdala and autism: implications from non-human primate studies

Brothers (1990) has proposed that the amygdala is an important component of the neural network that underlies social behavior. Kemper and Bauman (1993) identified neuropathology in the amygdala of the postmortem autistic brain. These findings, along with recent functional neuroimaging data, have led Baron-Cohen et al. (2000) to propose that dysfunction of the amygdala may be responsible, in part, for the impairment of social behavior that is a hallmark feature of autism. Recent data from studies in our laboratory on the effects of amygdala lesions in the adult and infant macaque monkey do not support a fundamental role for the amygdala in social behavior. If the amygdala is not essential for the component processes of social behavior, as seems to be case in both non-human primates and selected patients with bilateral amygdala damage, then it is unlikely to be the primary substrate for the impaired social behavior of autism. However, damage to the amygdala does have an effect on a monkey's response to normally fear-inducing stimuli, such as snakes, and removes a natural reluctance to engage novel conspecifics in social interactions. These findings lead to the conclusion that an important role for the amygdala is in the detection of threats and mobilizing an appropriate behavioral response, part of which is fear. Interestingly, an important comorbid feature of autism is anxiety (Muris et al. 1998). If the amygdala is pathological in subjects with autism, it may contribute to their abnormal fears and increased anxiety rather than their abnormal social behavior.

Molecular genetics of autism spectrum disorders

Autistic disorder belongs to a broad spectrum of pervasive developmental disorders. Autism is a clinically and genetically heterogeneous condition. It is characterized by impairment in a broad range of social interactions, communication, and repetitive patterns of behavior and interest. Although the exact etiology of the condition is not known, family and twin studies strongly support genetic factors in autism. Genome-wide scans suggest several susceptibility loci that may contain one or more predisposing genes. However, no such genes have been identified so far that predispose patients to autism. The condition is over 90% heritable, but the mode of inheritance is not clear. Moreover, it does not seem to be a single gene disorder. There is no cure for autism. Individualized structured education, family support services, and antipsychotic drugs are recommended. These may alleviate some behavioral problems. The identification of autism genes, an understanding of the neurobiology of the condition, and additional clinical studies may help to develop pharmacological interventions in the future.

Genetic and neurodevelopmental influences in autistic disorder

OBJECTIVE

In the past, autism was considered to be largely psychogenic. However, research in the last 2 decades indicates that autism is largely caused by genetic factors that lead to abnormal brain development. This article reviews research into the genetic and neurodevelopmental factors underlying autism.

METHODS

We review the findings from genetic and brain-imaging studies of autism over the past 15 years and synthesize these findings as a guide for future research.

RESULTS

Genome scans and association studies have suggested potential genomic regions and genes, respectively, that may be involved in the etiology of autism, and there have been some replications of these results. Similarly, the findings that brain volume is exaggerated in autism and corpus callosum size is reduced have also been independently replicated. Unfortunately, studies of other subcortical structures remain inconclusive or contradictory.

CONCLUSIONS

Overwhelming evidence now supports a neurobiological basis for autism. However, further refinements will be needed to guide future studies, particularly to identify the most informative phenotypes to investigate. Additionally, studies examining the role of genetic factors in the brain abnormalities underlying autism will likely lead to further findings that will enhance our understanding of autism's causes.

Paradoxical autonomic response to mental tasks in autism

Autonomic responses to mental tasks requiring sustained attention were examined in individuals with autism and age- and ability-matched controls. Cardiac autonomic function (CAF) was evaluated based on heart rate variability. While the control group showed a significant decrease in the parasympathetic function during mental tasks, the autistic group showed no significant changes in CAF. When examined individually, parasympathetic function was suppressed in all subjects in the control group. On the other hand, parasympathetic function was activated in half of the autistic subjects. The paradoxical autonomic response suggests that some autistic subjects were more stressed under 'resting' conditions than while performing mechanical or repetitive mental tasks. The results seem to support autonomic hyperarousal in some people with autism.

Autism: a large unmet medical need and a complex research problem

Autism has been becoming the focus of attention as its apparently increasing prevalence is better appreciated. According to some estimates, the frequency of children with autistic spectrum disorder (ASD) can be as high as 1 in 150. The diagnosis can be made as early as 2 years of age, and autistic patients often have a normal life span. Thus, in terms of the number of "patient years," ASD represents a market that is as large as that of the biggest neurological indication, Alzheimer's disease. Despite the clear unmet medical need, no effective treatment is available. This may be because the mechanism of ASD is not understood. The aim of the present paper is to review recent advances in autism research and to discuss some of the most stressing problems mainly from a preclinical research standpoint. We hope to draw attention to the need to study this devastating disease that places an enormous burden on the society in general and the relatives and caregivers of autistic patients in particular.

The effect of cingulate lesions on social behaviour and emotion

Functional and structural neuroimaging of the human cingulate cortex has identified this region with emotion and social cognition and suggested that cingulate pathology may be associated with emotional and social behavioural disturbances. The importance of the cingulate cortex for emotion and social behaviour, however, has not been clear from lesion studies. Bilateral lesions in the cingulate cortex were made in three macaques and their social interactions were compared with those of controls. Subsequently, cingulate lesions were made in the three controls and their behaviour was compared before and after surgery. Cingulate lesions were associated with decreases in social interactions, time spent in proximity with other individuals, and vocalisations but an increase in manipulation of an inanimate object. The results are consistent with a cingulate role in social behaviour and emotion.

Object and spatial relational memory in adult rhesus monkeys is impaired by neonatal lesions of the hippocampal formation but not the amygdaloid complex

Adult rhesus monkeys with neonatal aspiration lesions of the hippocampal formation or the amygdaloid complex (including their respective subjacent cortices) and their age-matched controls were tested on the transverse patterning problem (A+ vs. B-, B+ vs. C- and C+ vs. A-) and a spatial version of the delayed nonmatching-to-sample (DNMS) task with delays of 10 s to 30 s, 60 s, 120 s, and 600 s. Monkeys with neonatal damage to the amygdaloid complex learned both tasks and did not differ from controls at any delay of the spatial DNMS task. Monkeys with neonatal hippocampal damage, however, were unable to learn transverse patterning, though they easily transferred to a linear series (A+ vs. B-, B+ vs. C-, and C+ vs. X-). Three of the four were also unable to reach criterion on the spatial DNMS task within the limits of testing, and the performance of all four monkeys deteriorated with increasing choice delays. The data suggest a role of the primate hippocampal region in both object and spatial relational learning.

The role of the fusiform face area in social cognition: implications for the pathobiology of autism

A region in the lateral aspect of the fusiform gyrus (FG) is more engaged by human faces than any other category of image. It has come to be known as the 'fusiform face area' (FFA). The origin and extent of this specialization is currently a topic of great interest and debate. This is of special relevance to autism, because recent studies have shown that the FFA is hypoactive to faces in this disorder. In two linked functional magnetic resonance imaging (fMRI) studies of healthy young adults, we show here that the FFA is engaged by a social attribution task (SAT) involving perception of human-like interactions among three simple geometric shapes. The amygdala, temporal pole, medial prefrontal cortex, inferolateral frontal cortex and superior temporal sulci were also significantly engaged. Activation of the FFA to a task without faces challenges the received view that the FFA is restricted in its activities to the perception of faces. We speculate that abstract semantic information associated with faces is encoded in the FG region and retrieved for social computations. From this perspective, the literature on hypoactivation of the FFA in autism may be interpreted as a reflection of a core social cognitive mechanism underlying the disorder.

Investigating individual differences in brain abnormalities in autism

Autism is a psychiatric syndrome characterized by impairments in three domains: social interaction, communication, and restricted and repetitive behaviours and interests. Recent findings implicate the amygdala in the neurobiology of autism. In this paper, we report the results of a series of novel experimental investigations focusing on the structure and function of the amygdala in a group of children with autism. The first section attempts to determine if abnormality of the amygdala can be identified in an individual using magnetic resonance imaging in vivo. Using single-case voxel-based morphometric analyses, abnormality in the amygdala was detected in half the children with autism. Abnormalities in other regions were also found. In the second section, emotional modulation of the startle response was investigated in the group of autistic children. Surprisingly, there were no significant differences between the patterns of emotional modulation of the startle response in the autistic group compared with the controls.

Non-human primate models of childhood psychopathology: the promise and the limitations

Although non-human primate models have been used previously to investigate the neurobiology of several sensory and cognitive developmental pathologies, they have been employed only sparingly to study the etiology of childhood psychopathologies for which deficits in social behavior and emotion regulation are major symptoms. Previous investigations of both adult human and non-human primates have indicated that primate social behavior and emotion are regulated by a complex neural network, in which the amygdala and orbital frontal cortex play major roles. Therefore, this review will provide information generated from the study of macaque monkeys regarding the timing of normal social and emotional behavior development, the normal pattern of anatomical and functional maturation of the amygdala and orbital frontal cortex, as well as information regarding the neural and behavioral effects of early perturbations of these two neural structures. We will also highlight 'critical periods' of macaque development, during which major refinements in the behavioral repertoire appear to coincide with significant neural maturation of the amygdala and/or orbital frontal cortex. The identification of these 'critical periods' may allow one to better predict the specific behavioral impairments likely to appear after neonatal damage to one or both of these neural areas at different time points during development. This experimental approach may provide a new and important way to inform and stimulate research on childhood psychopathologies, such as autism, schizophrenia and Williams syndrome, in which the development of normal social skills and emotional regulation is severely perturbed. Finally, the promise and limitations inherent to the use of non-human primate models of childhood psychopathology will be discussed.

Double-blind, placebo-controlled study of L-carnosine supplementation in children with autistic spectrum disorders

L-Carnosine, a dipeptide, can enhance frontal lobe function or be neuroprotective. It can also correlate with gamma-aminobutyric acid (GABA)-homocarnosine interaction, with possible anticonvulsive effects. We investigated 31 children with autistic spectrum disorders in an 8-week, double-blinded study to determine if 800 mg L-carnosine daily would result in observable changes versus placebo. Outcome measures were the Childhood Autism Rating Scale, the Gilliam Autism Rating Scale, the Expressive and Receptive One-Word Picture Vocabulary tests, and Clinical Global Impressions of Change. Children on placebo did not show statistically significant changes. After 8 weeks on L-carnosine, children showed statistically significant improvements on the Gilliam Autism Rating Scale (total score and the Behavior, Socialization, and Communication subscales) and the Receptive One-Word Picture Vocabulary test (all P < .05). Improved trends were noted on other outcome measures. Although the mechanism of action of L-carnosine is not well understood, it may enhance neurologic function, perhaps in the enterorhinal or temporal cortex.

Effects of genetic background on neonatal Borna disease virus infection-induced neurodevelopmental damage. I. Brain pathology and behavioral deficits

The pathogenic mechanisms of gene-environment interactions determining variability of human neurodevelopmental disorders remain unclear. In the two consecutive papers, we used the neonatal Borna disease virus (BDV) infection rat model of neurodevelopmental damage to evaluate brain pathology, monoamine alterations, behavioral deficits, and responses to pharmacological treatments in two inbred rat strains, Lewis and Fisher344. The first paper reports that despite comparable virus replication and distribution in the brain of both rat strains, neonatal BDV infection produced significantly greater thinning of the neocortex in BDV-infected Fisher344 rats compared to BDV-infected Lewis rats, while no strain-related differences were found in BDV-induced granule cell loss in the dentate gyrus of the hippocampus and cerebellar hypoplasia. Unlike BDV-infected Lewis rats, more severe BDV-induced brain pathology in Fisher344 rats was associated with (1) greater locomotor activity to novelty and (2) impairment of habituation and prepulse inhibition of the acoustic startle response. The present data demonstrate that the same environmental insult can produce differential neuroanatomical and behavioral abnormalities in genetically different inbred rat strains.

Neural systems involved in "theory of mind"

What is the nature of our ability to understand and reason about the beliefs of others--the possession of a "theory of mind", or ToM? Here, we review findings from imaging and lesion studies indicating that ToM reasoning is supported by a widely distributed neural system. Some functional components of this system, such as language-related regions of the left hemisphere, the frontal lobes and the right temporal parietal cortex, are not solely dedicated to the computation of mental states. However, the system also includes a core, domain-specific component that is centred on the amygdala circuitry. We provide a framework in which impairments of ToM can be viewed in terms of abnormalities of the core system, the failure of a co-opted system that is necessary for performance on a particular set of tasks, or the absence of an experiential trigger for the emergence of ToM.

Amygdala or ventral hippocampal lesions at two early stages of life differentially affect open field behaviour later in life; an animal model of neurodevelopmental psychopathological disorders

Psychiatric disorders like schizophrenia or autism are thought to result from disruption of the normal pattern of brain development. Abnormalities in the amygdaloid complex and hippocampus have been reported in these disorders. In the present study rats were lesioned in the amygdala or ventral hippocampus on day 7 of life (immature brain) or day 21 of life (almost mature brain) and open field behaviour was determined later in life before and after puberty. Lesioning on day 7 resulted in behavioural changes, interpreted as locomotor stereotypy and decreased anxiety in case of amygdala or hippocampus, respectively. These effects were more profoundly present after puberty. Lesioning on day 21 did not result in these behavioural changes, which subscribes to the importance of the stage of brain maturation on functional development. The results suggest that the behavioural changes in rats lesioned on day 7 may due to a malfunctioning of structures connected to the amygdala or ventral hippocampus. Brain lesions made on day 7 of life may serve as a potential model of psychopathological neurodevelopmental disorders.

Social interest and the development of cortical face specialization: what autism teaches us about face processing

Investigations of face processing in persons with an autism spectrum disorder (ASD) inform upon theories of the development of "normal" face processing, and the story that emerges challenges some models of the nature and origin of cortical face specialization. Individuals with an ASD possess deficits in face processing and a lack of a fusiform face area (FFA). Evidence from studies of ASD can be conceptualized best using an expertise framework of face processing rather than models that postulate a face module in the fusiform gyrus. Because persons with an ASD have reduced social interest, they may fail to develop cortical face specialization. Face specialization may develop in normal individuals because they are socially motivated to regard the face, and such motivation promotes expertise for faces. The amygdala is likely the key node in the system that marks objects as emotionally salient and could be crucial to the development of cortical face specialization.

The amygdala and related structures in the pathophysiology of autism

Autism is a neurodevelopmental disorder that is defined behaviorally by severe deficiencies in reciprocal social interaction, verbal and nonverbal communication, and restricted interests. The amygdala is involved in the regulation of social behaviors and may be an important site of pathology for the social dysfunction seen in autism. This review focuses on lesion, postmortem, and neuroimaging studies that investigate the amygdala and related structures in this disorder. Other brain regions potentially involved in the neuropathology of autism are also briefly discussed. Although supportive evidence exists for amygdala dysfunction in autism, the currently available data are inconsistent and additional research is needed.

Increased social fear and decreased fear of objects in monkeys with neonatal amygdala lesions

The amygdala has been implicated in the mediation of emotional and species-specific social behavior (Kling et al., 1970; Kling and Brothers, 1992; Kluver and Bucy, 1939; Rosvold et al., 1954). Humans with bilateral amygdala damage are impaired in judging negative emotion in facial expressions and making accurate judgements of trustworthiness (Adolphs et al., 1998, 1994). Amygdala dysfunction has also been implicated in human disorders ranging from social anxiety (Birbaumer et al., 1998) to depression (Drevets, 2000) to autism (Bachevalier, 1994; Baron-Cohen et al., 2000; Bauman and Kemper, 1993). We produced selective amygdala lesions in 2-week-old macaque monkeys who were returned to their mothers for rearing. At 6-8 months of age, the lesioned animals demonstrated less fear of novel objects such as rubber snakes than age-matched controls. However, they displayed substantially more fear behavior than controls during dyadic social interactions. These results suggest that neonatal amygdala lesions dissociate a system that mediates social fear from one that mediates fear of inanimate objects. Furthermore, much of the age-appropriate repertoire of social behavior was present in amygdala-lesioned infants indicating that these lesions do not produce autistic-like behavior in monkeys. Finally, amygdala lesions early in development have different effects on social behavior than lesions produced in adulthood.

Molecular genetics and animal models in autistic disorder

Autistic disorder is a behavioural syndrome beginning before the age of 3 years and lasting over the whole lifetime. It is characterised by impaired communication, impaired social interactions, and repetitive interests and behaviour. The prevalence is about 7/10,000 taking a restrictive definition and more than 1/500 with a broader definition, including all the pervasive developmental disorders. The importance of genetic factors has been highlighted by epidemiological studies showing that autistic disorder is one of the most genetic neuropsychiatric diseases. The relative risk of first relatives is about 100-fold higher than the risk in the normal population and the concordance in monozygotic twin is about 60%. Different strategies have been applied on the track of susceptibility genes. The systematic search of linked loci led to contradictory results, in part due to the heterogeneity of the clinical definitions, to the differences in the DNA markers, and to the different methods of analysis used. An oversimplification of the inferred model is probably also cause of our disappointment. More work is necessary to give a clearer picture. One region emerges more frequently: the long arm of chromosome 7. Several candidate genes have been studied and some gave indications of association: the Reelin gene and the Wnt2 gene. Cytogenetical abnormalities are frequent at 15q11-13, the region of the Angelman and Prader-Willi syndrome. Imprinting plays an important role in this region, no candidate gene has been identified in autism. Biochemical abnormalities have been found in the serotonin system. Association and linkage studies gave no consistent results with some serotonin receptors and in the transporter, although it seems interesting to go further in the biochemical characterisation of the serotonin transporter activity, particularly in platelets, easily accessible. Two monogenic diseases have been associated with autistic disorder: tuberous sclerosis and fragile X. A better knowledge of the pathophysiology of these disorders can help to understand autism. Different other candidate genes have been tested, positive results await replications in other samples. Animal models have been developed, generally by knocking out the different candidate genes. Behaviour studies have mainly focused on anxiety and learning paradigms. Another group of models results from surgical or toxic lesions of candidate regions in the brain, in general during development. The tools to analyse these animals are not yet standardised, and an important effort needs to be undertaken.

Anterior insular cortex: linking intestinal pathology and brain function in autism-spectrum subgroups

Autism includes deficits in communications skills and is associated with intestinal pathology. Numerous parents and some physicians report that an autistic child's attention and language improve in response to treatments which eliminate certain dietary antigens and/or which improve intestinal health. For at least some autism-spectrum children, the link between intestinal pathology, attention, and language may derive from shared neuroanatomic pathways within the anterior insular cortex (aIC); from a neurotrophic virus such as herpes simplex (HSV) migrating within afferents to the insular cortex; and/or from synaptic exhaustion in the aIC as induced by chronically inappropriate neuronal activity in the enteric nervous system and/or its vagal efferents.

Functional genomics approaches to a primate model of autistic symptomology

Several studies indicate a primary dysfunction of the temporal lobe in autism, specifically the hippocampal formation and entorhinal cortex (EC). Assessment of gene expression in the EC and hippocampus will provide insight into the subtle alterations in neuronal function associated with autism. To this end, evaluations in a primate model of social attachment, which produces behaviors associated with autism, in addition to the use of human post-mortem tissue from individuals diagnosed with autism will provide heretofore unattainable information of how the complex neural circuitry of this region is altered in autism. Identification of altered expression of multiple genes should provide a molecular "fingerprint" of autism and may provide new targets for pharmacotherapeutic intervention.

Adaptation and habituation to an open field and responses to various stressful events in animals with neonatal lesions in the amygdala or ventral hippocampus

A rat model of neurodevelopmental psychopathological disorders, designed to determine neurodevelopmental deficits following damage to the brain early in life, was used to investigate behavioural changes in adaptation and habituation to an open field and responses to different kinds of stressful events. Animals with bilateral ibotenic acid lesions in the amygdala or ventral hippocampus on day 7 or 21 of life were compared to sham-operated animals. According to the model it was assumed that behavioural changes in animals lesioned on day 7, but not in animals lesioned on day 21 of life, were caused by maldevelopment of one or more structures connected to the damaged area. Animals lesioned in the amygdala or ventral hippocampus on day 7, but not animals lesioned in these structures on day 21 of life, displayed decreased (within-session) adaptation and (between-session) habituation to the open field and a decrease in immobility in the forced swim test, whereas only animals lesioned in the amygdala displayed enhanced general activity. These results were indicative of neurodevelopmental deficits. No changes in stress-induced hyperthermia were found, while animals lesioned in the amygdala both on day 7 or 21 of life exhibited decreased conditioned ultrasonic vocalizations. These latter results suggest that the amygdala is implicated in the conditioned stress-induced response. The contribution of the present findings to the animal model of neurodevelopmental disorders like schizophrenia and possible brain structures and neurotransmitter systems involved in the neurodevelopmental deficits are discussed.

Autonomic responses of autistic children to people and objects

Several recent lines of inquiry have pointed to the amygdala as a potential lesion site in autism. Because one function of the amygdala may be to produce autonomic arousal at the sight of a significant face, we compared the responses of autistic children to their mothers' face and to a plain paper cup. Unlike normals, the autistic children as a whole did not show a larger response to the person than to the cup. We also monitored sympathetic activity in autistic children as they engaged in a wide range of everyday behaviours. The children tended to use self-stimulation activities in order to calm hyper-responsive activity of the sympathetic ('fight or flight') branch of the autonomic nervous system. A small percentage of our autistic subjects had hyporesponsive sympathetic activity, with essentially no electrodermal responses except to self-injurious behaviour. We sketch a hypothesis about autism according to which autistic children use overt behaviour in order to control a malfunctioning autonomic nervous system and suggest that they have learned to avoid using certain processing areas in the temporal lobes.

Antiepileptic drugs: affective use in autism spectrum disorders

Antiepileptic drugs are widely administered to individuals with autistic spectrum disorders. There are several reasons for the use of antiepileptic drugs in autistic spectrum disorders, including the high incidence of epilepsy in these individuals, the anecdotal reports suggesting an improvement of communication and behavior in autistic subjects with epileptic discharges, and the increased awareness that some disruptive behaviors may be manifestations of an associated affective disorder. In this study, data on the current use of antiepileptic drugs in the treatment of autism, and on the association of affective disorders with epilepsy and autism, are reviewed. The evidence supporting the hypothesis that there may be a subgroup of autistic children with epilepsy and affective disorders that preferentially respond to antiepileptic drugs is still very preliminary, and further investigations with double-blind controlled studies are needed. Although the role of antiepileptic drugs at the present time is not established, there is evidence that autism, epilepsy, and affective disorders commonly co-occur, and that they may share a common neurochemical substrate, which is the common target of the psychotropic mechanism of action of different antiepileptic drugs.

Judgments of social appropriateness by children and adolescents with autism

Children and adolescents with autism (autism group, n = 19) and those without autism (Nonautism group, n = 19) of similar age and IQ were asked to make judgments of the social appropriateness of 24 videotaped, staged scenes with adult actors. Each scene depicted an appropriate or an inappropriate interaction. Half contained verbalizations, and half did not. After each scene, the participant was asked: (1) Was that o.k. or was something wrong with it? If the participant judged the scene was wrong, she or he was asked: (2) What was wrong with it?; and (3) Why was that wrong? Both groups correctly identified inappropriate behaviors most of the time, and correct behaviors almost all of the time. However, the Nonautism group detected inappropriate behaviors significantly more often than the Autism group, for verbal but not nonverbal scenes. It was also significantly easier for both groups to identify inappropriate behaviors in the nonverbal than in the verbal scenes. Ratings of the explanations given for Question 3 differed significantly between the groups for verbal but not for nonverbal scenes, with Nonautism participants more likely to give explanations involving social norms and principles, and the Autism group more likely to give explanations that were irrelevant or idiosyncratic.